This invention relates to a process for making media for receiving jetted ink in which photo-resist and etching steps are employed to create a hydrophobic array on an ink-absorbing media.
Prints made using an ink-jet printer desirably have image resolution of about 6 line pairs/mm, which corresponds to about 84 xcexcm per line or equivalently about 300 dots per inch. They must have a dynamic range of about 128 gray levels or more in order to be comparable in image quality to conventional photographic prints.
Secondary colors are formed as combinations of primary colors. The subtractive primary colors are cyan, magenta and yellow and the secondary ones are red, green and blue. Gray can be produced by equal amounts of cyan magenta and yellow, but less fluid is deposited on the paper if the gray is produced from an ink supply containing only black dye or pigment.
Consider a typical print head emitting 4 pL drops and that a saturated spot of a secondary color is to be formed. The 4 pL droplet has a diameter of about 20 xcexcm in the air and forms a disk of about 30 xcexcm on the paper. Adjacent droplets are typically aimed to be placed on 21 xcexcm centers so that adjacent disks on the paper have some overlap and thus ensure that full area coverage is obtained and that jet misdirections do not produce visible artifacts. Then, as taught in U.S. Pat. No. 6,089,692, of Anagnostopoulos, if a saturated spot of a secondary color is to be formed, at least 256 droplets (128 of each of the primary colors) have to be deposited per 84xc3x9784 xcexcm2 area. The amount of fluid deposited per unit area is then about 145 mL/m2. The problem, however, is that this is at least a factor of 6 higher than the fluid holding capacity of commercial photo-grade ink-jet papers. See for example Kenzo Kasahara, xe2x80x9cA New Quick-Drying, High-Water Resistant Glossy Ink Jet paper,xe2x80x9d Proceedings ISandT""s NIP 14: 1998 International Conference on Digital printing Technologies, Toronto, Canada, Oct. 18-23, 1998, pp 150-152.
One way of solving this first problem is to increase the fluid capacity of the ink-jet paper by increasing the thickness of the image-receiving layer. This is typically not advisable because color saturation and image resolution are reduced since the dyes diffuse too far below the surface. Another way of increasing the apparent fluid holding capacity is to allow some evaporation to take place before depositing additional droplets. This increases the printing time and is thus also not acceptable. A third solution is to have inks available at the print head of different colorant concentrations. Thus, the high color density areas are printed with dots that have high concentration of colorant while the light color areas on the print are made with low colorant concentration droplets. This approach substantially increases the cost to the consumer and is thus also not an acceptable solution. Furthermore, the image quality is not photographic when a limited choice of ink colorant densities are available at the print head.
A second problem with regards to producing photographic quality ink-jet prints is that the penetration rate of ink into the image-receiving layer of presently available porous or swellable commercial receivers is too low. This is because the media are purposely made to have small surface pores in order to have a glossy finish. Consequently the printing algorithms are written such that they do not allow a droplet to be placed on top or adjacent to another droplet until sufficient time has elapsed. This results in slow printing time and is therefore unacceptable. If an attempt is made to print faster, coalescence and color bleed are observed. That is, the small pores prevent the first ink droplet from being absorbed into the paper quickly enough and, if the next droplet arrives too soon, the two merge or coalesce into one large one. This reduces the image resolution. Color bleed is essentially the same effect as coalescence, except that the two droplets that merge contain different color colorants. The effect is poor image sharpness and color quality.
There are a large number of commercial ink-jet papers. Two of the most successful are described briefly here. The first is shown in FIG. 1. The receiver, as described in U.S. Pat. No. 6,045,917 of Missell et al., consists of a plain paper base covered by a polyethylene coat. This coat prevents any fluid, especially water from the ink, from penetrating into the paper base and causing puckering or wrinkling termed xe2x80x9ccocklexe2x80x9d. The front side of the paper is additionally coated with two layers of polymers containing mordant. The polymer layers absorb the ink by swelling while the dyes are immobilized in the mordant. An anti-curl layer is also coated in the backsides of this paper.
The second commercial paper is described by Kenzo Kasahara, in xe2x80x9cA New Quick-Drying, High-Water Resistant Glossy Ink Jet paper,xe2x80x9d Proceedings ISandT""s NIP 14: 1998 International Conference on Digital printing Technologies, Toronto, Canada, Oct. 18-23, 1998, pp 150-152, and is shown in FIG. 2. Like the first paper, the paper base is coated with a polyethylene film to prevent cockle. The image-receiving layer consists of three separate layers. Each one is made up of ICOS (inorganic core/organic shell) particles in a polyvinyl alcohol binder and boric acid hardener, forming a micro-porous structure. The porosity of all three layers combined is about 25 ml/m2. Each of the ICOS particles, of the order of 0.05 xcexcm in diameter, consists of an anionic silica core surrounded by a cationic polymer shell.
Other recent articles describe ink jet papers with surface pores or micro-capillaries formed by alumina or silica particles (see for example Aidan Lavery, xe2x80x9cPhotomedia for Ink Jet printing,xe2x80x9d Proceedings ISandTs NIP16: 2000, International Conference on Digital Printing Technologies, Vancouver Canada, October 16-20, 2000, pp 216-220) or micels (see for example Dieter Reichel and Willy Heinzelmann, xe2x80x9cAnisotropic porous Substrates for High Resolution Digital Images,xe2x80x9d Proceeding ISandTs NIP16: 2000 International Conference on Digital Printing Technologies, Vancouver Canada, Oct. 16-20, 2000, pp 204-207). In all these cases the goal is to rapidly move the fluid, through capillary action, below the surface so as to reduce coalescence and color bleed, which occurs mostly at the surface. None of these, however, move the fluid fast enough to meet the productivity needs required for photographic quality prints.
Inkjet print heads have been recently invented that are page wide and have nozzle spacing of finer than 300 per inch. See, for example, U.S. Pat. No. 6,079,821, of Chwalek et al. Such print heads produce 1 to 2 pL drops which are smaller than the typical droplets produced by the commercial print heads. Also, because they are page wide and have a large number of nozzles, they are capable of ink lay down rates substantially higher than that of the scanning type conventional ink-jet printers. But coalescence and color bleed at the receiver surface compromise their productivity. This constitutes the third problem, namely that the present receiver media seriously limit the productivity of these advanced print heads.
Finally, for desired resolution and color saturation, the colorant should reside within only a few microns from the surface of the receiver.
A need exists for making an image receiver media that is capable of accepting fluid lay down quantities that exceed the amount their image receiving layer can hold and that allow a droplet to be placed simultaneously on top or adjacent to a previous one without coalescence or color bleed between adjacent droplets.
The invention provides a media for receiving jetted ink containing imaging colorant, comprising a support bearing a predetermined array of three dimensional cells composed of hydrophobicwalls and having a hydrophilic base, the cross-section of the cells parallel to the support being of a size sufficiently small so as to improve the range of color saturation attainable.
Embodiments of the invention are capable of accepting fluid lay down quantities that exceed the amount their image receiving layer can hold and that allow a droplet to be placed simultaneously on top or adjacent to a previous one without coalescence or color bleed between adjacent droplets.